A conventional two-stage turbocharger apparatus compresses intake air twice and supplies the compressed intake air to a combustion chamber of an engine, thereby enabling power of the engine to be increased. In addition, it may be possible to minimize an energy loss of exhaust gas by maximizing efficiency of the two-stage turbocharger apparatus through high and low pressure turbochargers connected in series.
FIG. 1 is a diagram illustrating a structure of a typical two-stage turbocharger apparatus of an engine. Referring to FIG. 1, the two-stage turbocharger apparatus includes a high-pressure side turbo device 12 connected to an exhaust manifold 11a and an intake manifold 11b of an engine 11, and a low-pressure side turbo device 13 connected in series thereto.
In addition, a high-pressure turbine TB1 of the high-pressure side turbo device 12 and a low-pressure turbine TB2 of the low-pressure side turbo device 13 rotate using flow energy of exhaust gas discharged from the exhaust manifold 11a of the engine 11. Through such a configuration, air is primarily pressurized by a low-pressure compressor CP2 of the low-pressure side turbo device 13 and the air is secondarily pressurized by a high-pressure compressor CP1 of the high-pressure side turbo device 12, so that the pressurized air is supplied to the intake manifold 11b of the engine through an intercooler 14.
When the engine 11 is driven at high speed, the amount of exhaust gas taken in by the high-pressure side turbo device 12 is insufficient compared to an amount of exhaust gas discharged from the exhaust manifold 11a. For this reason, a waste gate valve WG mounted to the high-pressure turbine TB1 is opened such that exhaust gas is bypassed.
When an Exhaust Gas Recirculation (EGR) valve 15 is opened, the exhaust gas recirculated by the EGR valve 15 is cooled through an EGR cooler.
In this case, there is however a problem in that performance of the two-stage turbocharger apparatus may not be maximized under some operating conditions such as high EGR rate since pressure decrease occurs at an inlet of the high-pressure turbine TB1 when the EGR valve 15 is opened and the volume of a passage connected to the low-pressure turbine TB2 is increased when the waste gate valve WG is also opened.
In particular, when the EGR valve 15 is widely opened, the efficiency of the high-pressure turbine TB1 may be decreased due to flow separation at the inlet end of the high-pressure turbine TB1. For this reason, the efficiency of the two-stage turbocharger apparatus may be reduced since a boost pressure rising rate is decreased when a vehicle is accelerated.
The matters described as the related art have been provided only for assisting the understanding for the background of the present inventive concept and should not be considered as corresponding to the related art already known to those skilled in the art.